Electron beam scanning device for symbol and graphical information

ABSTRACT

A plurality of control plates are sandwiched between an area electron source and a target, such control plates having apertures formed therein, the apertures of successive plates being aligned to form a plurality of electron channels between the electron source and the target. First control plates are utilized to direct electrons to a selected area of the target and have a first and second set of control electrodes arranged in parallel strips thereon, the first set of strips being orthogonal to the second set. The electrode strips each encompass a plurality of rows or columns of the apertures and thus define the height and width of the characters to be displayed. Second control plates are utilized to form the symbols to be displayed and have apertures formed therein aligned with the apertures of the first control plates to form a portion of the electron channels between the electron source and the target. The second control plates have mutually orthogonal strip electrodes formed thereon which are selectively energized to permit electrons to pass through portions thereof so as to define the symbols to be displayed.

United States Patent Goede et a1.

[54] ELECTRON BEAM SCANNING DEVICE FOR SYMBOL AND GRAPHICAL INFORMATION [72] Inventors: Walter F. Goede; John E. Gunther, both of Torrance; Takeshi Noda, Los Angeles, all of Calif.

Northrop Corporation, Calif.

22 Filed: July 20,1970

211 Appl.No.: 56,330

[73] Assignee: Beverly Hills,

[ 1 Feb.29,1972

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorney-Sokolski & Wohlgemuth and W. M. Graham [5 7] ABSTRACT A plurality of control plates are sandwiched between an area electron source and a target, such control plates having apertures formed therein, the apertures of successive plates being aligned to form a plurality of electron channels between the electron source and the target. First control plates are utilized to direct electrons to a selected area of the target and have a first and second set of control electrodes arranged in parallel strips thereon, the first set of strips being orthogonal to the second set. The electrode strips each encompass a plurality of rows or columns of the apertures and thus define the height and width of the characters to be displayed. Second control plates are utilized to form the symbols to be displayed and have apertures formed therein aligned with the apertures of the first control plates to form a portion of the electron channels between the electron source and the target. The second control plates have mutually orthogonal strip electrodes formed thereon which are selectively energized to permit electrons to pass through portions thereof so as to define the symbols to be displayed.

9 Claims, 1 1 Drawing Figures SYMBOL 5 SYMBOL GENERATOR GENERATOR MODULATOR I PATENTEDFEB29 m2 SHEET 1 BF 4 FIG.|

SOi-OLSKI 8: WOHLGEMUTH FIG.3

ATTOR NEYS PATENTEUFEBZQ I972 3,646,382

SHEET 2 OF 4 MODULATOR SYMBOL GENERATOR 34 SYMBOL GENERATOR 33 SWITCHING VOLTAGE CONTROL SWITCHING VOLTAGE CONTROL IOOV- mvsmohs WALTER F GOEDE JOHN E. GUNTHER TAKESHI NODA OVOIJS SDKOLSKI 8| WOHLGEMUTH ATTORNEYS PATENTEDFEBZQ m2 3,646.382

SHEET 3 []F 4 U o o o o o o o o 0 4 0 o o o o 0 0 o 0 o o o o o o o o o o o o o o o o 0 o o o o o o 25 \ISQ SYMBOL GENERATOR --Lo 0 o o 0 i o FIGL o o o o L 123MB o I I Q 7a SYMBOL GENERATOR FIG. 5

INVENTORS WALTER E GOEDE JOHN E. GUNTHER TAKESHI NODA SXOLSKI 8a WOHLGEMUTH ATTORNEYS PAIENTEnFms 1972 SHEET '4 [1F 4 INVENTORS WALTER E GOEDE JOHN E. GUNTHER TAKESHI NODA SOKOLSKI 8r WOHLGEMUTH ATTORNFYQ ELECTRON BEAM SCANNING DEVICE FOR SYMBOL AND GRAPHICAL INFORMATION This invention relates to electron beam scanning devices and more particularly to such a device suitable or displaying graphical information or writing symbols of the alphanumeric type or the like on a target in response to digital control signals.

In US. Pat. No. 3,408,532 for an Electron Beam Scanning Device, assigned to Northrop Corporation, the assignee of the present application, an electron beam scanning device is described which utilizes a plurality of control plate members sandwiched between a cathode and a target which is of relatively flat and thin proportions. In this device, electron beam channels are formed between the cathode and the target by means of apertures in the successive control plates which are aligned with each other. As pointed out in this patent, this type of electron beam scanning device has distinct advantages over cathoderay scanners of the prior art in view of its compact proportions as compared with cathode-ray tubes, its capability of random addressing as compared with the cyclical type of scanning of cathode-ray tubes, and its operation in response to digital control signals. Further, the electron beam scanning device as described in the aforementioned patent is inherently capable of more accurate registration from the point of view of linearity and the fact that it is not readily affected by stray ambient magnetic and electrostatic fields as in the case of conventional cathode-ray tubes. This type of scanning device also has the inherent capability of being readily adapted to multibeam operation. It also can readily be utilized without significant circuit modification with beam penetration targets for color displays.

The device of the present invention utilizes the same basic scanning technique as described in U.S. Pat. No. 3,408,532 but utilizes different control plates for controlling the electron beam, this control means being particularly suited to the display of symbol information such as that of the alphanumeric type. The term symbol as used herein is also meant to include graphical display elements which combine to form a graphical display. The device of this invention is particularly suited to the display of information derived from digital equipment, such as for example in the readout display for a digital computer, in view of the fact that it responds directly to digital control signals. It thus is suitable for use in response to such digitally derived signals with a significantly smaller amount of conversion equipment as compared with conventional scanning cathode-ray tubes.

While certain displays for symbol and graphical information of relatively flat thin proportions have been developed, such as for example those of the plasma, Nixie tube and electroluminescent types, these devices have several shortcomings which are obviated by the present device. These shortcomings include the need for rather complicated electronics as compared with the device of this invention, limited flexibility in their operation in that they are not readily adaptable to multicolor displays and further the inability to respond to beam intensity modulation, i.e., to provide a display varying in its brilliance in accordance with control signals.

The device of this invention thus affords distinct advantages not only over conventional cathode-ray tube displays but also flat plate symbol displays of the prior art in its capability of operating with relatively simple input electronics, its inherent ability to be adapted to multicolor display, and its ability to respond to intensity modulation signals.

It is therefore the principal object of this invention to provide an improved electron beam scanning device of relatively thin compact proportions, which is capable of displaying, storing, or memorizing symbol or graphical information in response to regular or random digital addressing symbols.

Other objects of this invention will become apparent from the following description taken in connection with the accompanying drawings, of which:

FIG. I is a perspective view illustrating one embodiment of the device of the invention,

FIG. 2 is a schematic exploded view illustrating the embodiment of FIG. I,

FIG. 3 is a cross-sectional view partially in section taken along the plane indicated by 3-3 in FIG. 1,

FIG. 4 is a schematic view illustrating one of the symbol forming control plates of the embodiment of FIG. 1,

FIG. 5 is a schematic view illustrating the other of the symbol control plates of the embodiment of FIG. I, and

FIG. 6A-6E are schematic views illustrating the formation of a symbol with the device of the invention.

Briefly described, the device of the invention comprises an area electron source and a target between which are sandwiched a plurality of control plates for controlling the flow of electrons therebetween. The control plates have a plurality of apertures extending therethrough, such apertures being arranged in rows and columns, the apertures on successive plates being aligned with each other to form electron beam channels running between the electron source and the target. First of the control plates which are utilized for directing the electrons to a selected area of the target have a first set of electrodes arranged in parallel strips and encompass a plurali ty of rows of the apertures formed therein and a second set of electrodes arranged in parallel strips orthogonal to the first set, each such strip encompassing a plurality of columns of the apertures. Digital control means are connected to the electrodes and selectively apply potentials to the control electrodes so as to permit electrons to pass through to an area of the target on which a symbol is to be written. Second of the control plates are provided for forming the symbols to be displayed and have apertures formed therein corresponding to those of the first control plates and aligned therewith to form a portion of the electron channels. The second of the control plates include first and second sets of control electrodes arranged in mutually orthogonal sets running substantially parallel respectively to the first and second sets of control electrodes of the first control plates. These strips each encompass a single row or column of apertures. The strips of the symbol forming control plates are driven by digital control signals to define the symbols or graphical elements to be formed.

In this manner, electron beams can be digitally addressed to a selected portion of the target and symbols formed on this selected portion of the target in response to digital control signals. It is to be noted that the device of the invention could be utilized to control not only electron beams but also beams of other charged particles, such as positive or negative ions.

Referring now to FIGS. 1 and 3 the structural features of one embodiment of the device of the invention are illustrated. Sandwiched between area electron source 11 and target member 12 are a plurality of control plates 14-18. The cathode target and control plates are contained within an airtight casing formed by frame 21 and the cathode and target. This casing being evacuated to provide a vacuum environment. The control plates and the cathode and target are separated from each other by means of separator strips 22 which may be of dielectric material such as glass or ceramic and are positioned along the edges of the plates.

Area electron source 11 may be a cathode plate having one surface thereof coated with radioactive material or may be a thermionic cathode. Target 12 where the device is utilized for display purposes may comprise a glass plate having a phosphorescent coating 12a thereon. Where the device is used as a memory, the target may comprise a storage target plate. In the case of a color display, the target may comprise a beam penetration phosphor. The control plates l4l8 have apertures 25 extending through the broad surfaces thereof, corresponding apertures on successive plates being aligned with each other to form a plurality of electron beam channels between the cathode and the target. The surfaces of apertures 25 are preferably coated with a resistive material which may also be secondary emissive as described in the aforementioned U.S. Pat. No. 3,408,532, the resistive coatings interconnecting the electrodes on the opposite surfaces of the control plates. A secondary emissive material such as lead oxide or tin oxide may be utilized. Where secondary emissive material is utilized to provide electron multiplication, apertures 25 are preferably canted in opposite directions from control plate to control plate as indicated in FIG. 3, thereby to increase the incidence of electrons against the secondary emissive surfaces and thus improve the electron multiplication and to make for better cutoff action when the channels are biased off. The surfaces of the apertures may also be made fully conductive if a potential differential is not applied between the electrodes on the opposite surfaces of the control plates, the voltage gradient for accelerating the electrons being established between successive control plates.

Control plates 14-18 have electrodes l4a-18a and 14b-18b on the opposite broad surfaces thereof. Electrodes 14a-17a are arranged in a predetermined strip pattern as to be described in connection with FIGS. 2, 4 and 5, and are utilized to direct the electron beam to predetermined portions of the target. Electrodes l4b-l8b and 18a cover substantially the entire surface area of the plates encompassed by apertures 25. Control plates 14-18 are of dielectric material such as glass or suitable ceramic. The control electrodes Mil-18a and 14b-18 should be of a highly conductive material such as gold which may be deposited on the surfaces of the dielectric substrate Referring now to FIG. 2, an exploded view of the embodiment of FIG. 1 is schematically illustrated. Control plate 14 has a plurality of control electrodes 14a on one surface thereof, these electrodes being arranged in horizontal strips which are separated from each other by a predetermined spacing. Control electrode has a plurality of electrodes 15a formed on one surface thereof, these electrodes being arranged in vertical strips which are separated from each other. Strips 14a and 15a, which are utilized to direct the electron beam to a particular area of the target on which a symbol is to be displayed, form a matrix having a plurality of matrix elements 30 defining discrete symbol display areas, each such element having a vertical dimension defined by the width of strips 14a, and a horizontal dimension defined by the width of strips 151:. The spaces between matrix elements 30 which define the spacing between the symbols to be displayed and between rows of such symbols are preferably devoid of apertures so as to avoid electron flow in these areas and the unnecessary dissipation of energy incidental thereto.

Electrodes 14a are each connected to a separate voltage switching output of switching voltage control 33, while electrodes 15a are each connected to a separate switching voltage output of switching voltage control 34. Switching voltage controls 33 and 34 are adapted to provide a forward biasing potential between a selected one or more of electrodes 14a and electrode 14b and a selected one or more of electrodes 15a and electrode 15b in response to control signals so as to activate desired portions of the target. A back biasing potential is provided to the remaining electrode strips to deactivate the areas encompassed thereby. A fixed bias potential is applied at all times to electrodes 14!) and 15b, these potentials being gradated to enable the acceleration of electrons towards the target.

To illustrate the operation of the device, an example of a particular set of switching potentials operating to activate the matrix element encompassing the upper left-hand corner of the target are shown opposite the various leads from switching voltage controls 33 and 34. In the illustrative example the top one of strips 140 has a potential of 300 volts thereon which provides a forward bias relative to plate 14b (100 volts) while the remaining electrode strips have 75 volts applied thereto which provides a reverse bias to prevent the flow of electrons through their associated apertures. The far left-hand one of strips 15a has a forward biasing potential of 600 volts relative to electrode 15b (400 volts) while the remaining electrodes 150 have a reverse biasing potential thereon (375 volts). Thus, while electrons will be permitted to pass through all of the apertures in the top row of electrode strips 14a the continued passage of these electrons toward the target will be prevented in all but the portion thereof which is opposite the far lefthand one of control electrodes 150. In this manner electrons will be permitted to pass through only the matrix element 30 in the upper left-hand corner of the control plates. in a similar manner, by applying forward potentials to various other combinations of electrode strips 14a and 150, any desired matrix element 30 can be activated in a regular or random fashion.

Control plates 16 and 17, as to be described fully in connection with FIGS. 4 and 5, have a plurality of control electrodes 16a and 17a arranged in horizontal and vertical strips respectively. Each strip 16a encompasses a row of apertures 25, while each strip 170 encompasses a column of apertures. Strips 16a are arranged in groups of seven, each such group having a width corresponding to that of electrodes 14a, while strips 17a are arranged in groups of five each such group having a width corresponding to the width of electrodes 15a. As to be explained in connection with FIGS. 4 and 5, corresponding strips of each group of strips of control plates 16 and 17 are connected together. The electrode strips 16a of control plate 16 are connected to receive control potentials from symbol generator 36 while the electrode strips 17a of control plate 17 are connected to receive control potentials from symbol generator 37.

To illustrate how symbol generators 36 and 37 operate to form symbols to be displayed, the particular control voltage outputs from symbol generators 36 and 37 for energizing the electron beam 40 for the channel running to the extreme upper left-hand portion of the target 12 are shown. Thus, it can be seen that for energizing this particular portion of the target (and for corresponding portions of each of the other elemental areas 30 formed by control plates 14 and 15), the top row of electrodes 16:: is given a forward biasing potential (1,000 volts) relative to electrode 16b, while the remaining electrode strips have a reverse biasing potential (775 volts). At the same time the far left one of strip 17a has a forward biasing potential (1,300 volts) relative to electrodes 17b (1,100 volts), while the remaining electrodes 1711 have a reverse biasing potential (1,075 volts). It should immediately be apparent that by various combinations of voltages from symbol generators 36 and 37 that any portion of the matrix elements 30 can be activated in response to digital control signals.

Control plate 18 has overall electrodes 18a and 18b on both of the opposite surfaces thereof. This control plate is utilized for electron multiplication and/or for intensity modulating the beam in response to control signals from modulator 45. Thus, in the illustrative example, electrode 18b has a fixed potential of 1,400 volts thereon while electrode 18a receives a potential from modulator 45 which may vary around 1,600 volts in response to the intensity modulation signals so as to modulate the intensity of the beam. Target 12 has an acceleration potential thereon of 10 kv.

It is to be noted that electrodes 14a and 15a can be formed on opposite sides of a single plate and the electrodes 16a and 17a similarly formed on the opposite surfaces of a single plate, thus, combining the functions of two of the plates into one. This particular mode of implementation has been found, however, to have a disadvantage of crosstalk between channels and increased power dissipation in view of the extraneous currents set up in this type of implementation.

It is further to be noted that it is not necessary to modulate the beam and thus in such case plate 18 can be eliminated. Also, if so desired, the intensity modulation signals could be applied to plates 16 and 17 and plate 18 eliminated.

Referring now to FIGS. 4 and 5, the details of the electrodes of control plate 16 and 17 are schematically illustrated. As can be seen in FIG. 4, each of electrode strip 16a encompasses a single row of apertures 25. Further, as can be seen the electrode strips 16a are arranged in groups of seven rows which are separated from each other by a substantial space. Corresponding strips of each group are connected together, i.e., all the first strips are connected together, all the second strips are connected together, etc. Electrode strips 16a are connected to symbol generator 36 from which they receive signals for forming the symbols to be displayed.

Referring now to FIG. 5, electrode strips 170 are arranged in vertical columns normal to strips 16a and in groups of five, which are separated from each other. Corresponding columns of each group are connected together, i.e., all the first columns are connected together, all the second columns are connected together, etc. Electrode strips 170 receive symbol forming signals from symbol generator 37. It is to be noted that the information for forming each symbol is fed to a selected strip of each group of electrode strips simultaneously but that in view of the fact that only one of the elemental matrix areas of the target is selected at a time by means of control plates 14 and 15, the symbol will only be displayed in the selected portion of the target.

Referring now to FIG. 6A-6F, an illustrative example of the formation of a single symbol by means of control plates 16 and I7 is shown. A sign is shown for each of the strips 16a and 17a which are receiving a forward biasing potential at a particular moment in the symbol forming sequence The columns of dot patterns forming the symbols are formed in sequence in response to the signals received from symbol generators 36 and 37 which are sequentially fed to the electrode strips. The sequential formation of each of the dot pattern columns is shown successively in FIG. 6A-6E respectively. As can be seen in FIG. 6A, during the first time sequence, the first of strip columns 17a is forward biased, while the third through sixth of strip rows 16a are forward biased, all the remaining strips being reverse biased. With this particular set of control signals, five dots 48 as shown in FIG. 6A will be generated on display target 12 as shown in FIG. 6F. The second through fifth columns of the symbol will be similarly formed as shown in FIG. 6B-6E, respectively in response to the sequentially generated control signals. In this manner the letter A" is formed as shown in FIG. 6F. It should be apparent that any other letters, numerals, or symbols capable of being formed from the available dot pattern can be generated in similar fashion in response to various combinations of control signals.

It is to be noted that if so desired the entire target can be simultaneously activated by simultaneously placing forward biasing potentials on all of the strips of control plates 14-17; or particular areas of the target can be so energized. The capability to flood the target in this fashion is particularly useful in certain applications such as, where the target is a memory plate wherein such flooding is utilized to display information previously written on the target.

This invention thus provides a compact device suitable for displaying, storing or memorizing symbol or graphical information which responds directly to digital control signals and which is relatively simple and economical to implement in conjunction with digital computer outputs.

We claim:

1. A device for writing symbols on a target comprising:

an area charged particle source,

first control plate means interposed between said source and said target for directing charged particles from said source to a selected area of said target, said first control plate means having apertures formed therein arranged in rows and columns, said apertures defining channels between the source and target, said first control plate means further having a first set of control electrodes arranged in substantially parallel strips each encompassing a plurality of rows of said apertures to define the height of the symbols, and a second set of control electrodes arranged in substantially parallel strips each encompassing a plurality of columns of said apertures to define the width of the symbols,

second control plate means interposed between said source and said target for forming said symbols, said second control plate means having apertures formed therein which are aligned with corresponding apertures of said first con trol means and forming a portion of the channels defined thereby, said second control plate means further having first and second sets of control electrodes arranged in strips running substantially parallel respectively to the first and second sets of control electrodes of said first control plate means,

means for selectively applying potentials to the control electrodes of said first control plate means to permit the charged particles to pass through to an area of the target on which a symbol is to be written, and

means for selectively applying potentials to the control electrodes of said second control plate means to permit charged particles to pass through to the target to define the symbols to be written.

2. The device of claim 1 wherein said first and second con trol plate means each comprises a pair of plates, a separate set of said control electrodes being formed on one broad surface of each of said plates, the opposite broad surface of each of said plates having a single overall electrode thereon and a resistive material on the walls of said apertures interconnecting the electrodes on the opposite surfaces of said plates, said means for applying potentials to said control electrodes including means for applying a forward biasing potential between the ends of the apertures through which electron flow is desired.

3. The device of claim 2 wherein said resistive material is secondary emissive.

4. The device of claim 1 wherein the control electrodes of said second control plate means each encompass a single row and column of said apertures respectively.

5. In a device for writing symbols on a target including an area electron source and means for controlling the flow of electrons between said source and said target to form symbols on preselected portions of said target, comprising:

a plurality of control plates interposed between the electron source and the target with their broad surfaces aligned opposite each other,

said plates each having a plurality of apertures extending through their surfaces and arranged in rows and columns, corresponding apertures of successive control plates being aligned to form a plurality of electron channels running between the electron source and target,

first of said control plates being adapted to direct electrons to a selected area of the target and having first and second sets of control electrodes each such electrode set being arranged in strips on a separate one of the broad surfaces thereof, the strips of said first set being substantially orthogonal to those of said second set, said strips encompassing a predetermined number of rows and columns of said apertures and defining the width and height of the symbols,

means for selectively applying potentials to said electrodes to permit electrons to pass through to an area of the target in which a symbol is to be written,

second of said control plates being adapted to form said symbols and having first and second sets of control electrodes each such set being arranged in strips on a separate one of the broad surfaces thereof, the strips of said first set being substantially orthogonal to those of said second set, the strips of said first set each encompassing a row of said apertures, the strips of said second set each encompassing a column of said apertures, and

means for selectively applying potentials to the electrodes of the second of said control plates to permit electrons to pass through to portions of the areas selected by said first of said control plates so as to define the symbols to be written.

6. The device of claim 5 wherein said first and second control plates each comprises a pair of plates, a separate set of said control electrodes being formed on one broad surface of each of said plates, the opposite broad surface of each of said plates having a single overall electrode thereon and a resistive material on the walls of said apertures interconnecting the electrodes on the opposite surfaces of said plates, said means for applying potentials to said control electrodes including means for applying a forward biasing potential between the ends of the apertures through which electron flow is desired.

7. The device of claim 6 wherein said resistive material is 9. The device of claim wherein the electrode strips of said secondary emissive. second of said control plates positioned opposite correspond- 8. The device of claim 5 wherein the first and second sets of mg aperture Qoftions of the electrode P of said first of said control electrodes of said second of said control plates each control F connected Ogethef 50 as to form respectively encompass single rows and columns of said aper- 5 respondmg pomons of the symbols tures. 

1. A device for writing symbols on a target comprising: an area charged particle source, first control plate means interposed between said source and said target for directing charged particles from said source to a selected area of said target, said first control plate means having apertures formed therein arranged in rows and columns, said apertures defining channels between the source and target, said first control plate means further having a first set of control electrodes arranged in substantially parallel strips each encompassing a plurality of rows of said apertures to define the height of the symbols, and a second set of control electrodes arranged in substantially parallel strips each encompassing a plurality of columns of said apertures to define the width of the symbols, second control plate means interposed between said source and said target for forming said symbols, said second control plate means having apertures formed therein which are aligned with corresponding apertures of said first control means and forming a portion of the channels defined thereby, said second control plate means further having first and second sets of control electrodes arranged in strips running substantially parallel respectively to the first and second sets of control electrodes of said first control plate means, means for selectively applying potentials to the control electrodes of said first control plate means to permit the charged particles to pass through to an area of the target on which a symbol is to be written, and means for selectively applying potentials to the control electrodes of said second control plate means to permit charged particles to pass through to the target to define the symbols to be written.
 2. The device of claim 1 wherein said first and second control plate means each comprises a pair of plates, a separate set of said control electrodes being formed on one broad surface of each of said plates, the opposite broad surface of each of said plates having a single overall electrode thereon and a resistive material on the walls of said apertures interconnecting the electrodes on the opposite surfaces of said plates, said means for applying potentials to said control electrodes including means for applying a forward biasing potential between the ends of the apertures through which electron flow is desired.
 3. The device of claim 2 wherein said resistive material is secondary emissive.
 4. The device of claim 1 wherein the control electrodes of said second control plate means each encompass a single row and column of said apertures respectively.
 5. In a device for writing symbols on a target including an area electron source and means for controlling the flow of electrons between said source and said target to form symbols on preselected portions of said target, comprising: a plurality of control plates interposed between the electron source and the target with their broad surfaces aligned opposite each other, said plates each having a plurality of apertures extending through their surfaces and arranged in rows and columns, corresponding apertures of successive control plates being aligned to form a plurality of electron channels running between the electron source and target, first of said control plates being adapted to direct electrons to a selected area of the target and having first and second sets of control electrodes each such electrode set being arranged in strips on a separate one of the broad surfaces thereof, the strips of said first set being substantially orthogonal to those of said second set, said strips encompassing a predetermined number of rows and columns of said apertures and defining the width and height of the symbols, means for selectively applying potentials to said electrodes to permit electrons to pass through to an area of the target in which a symbol is to be written, second of said control plates being adapted to form said symbols and having first and second sets of control electrodes each such set being arranged in strips on a separate one of the broad surfaces thereof, the strips of said first set being substantially orthogonal to those of said second set, the strips of said first set each encompassing a row of said apertures, the strips of said second set each encompassing a column of said apertures, and means for selectively applying potentials to the electrodes of the second of said control plates to permit electrons to pass through to portions of the areas selected by said first of said control plates so as to define the symbols to be written.
 6. The device of claim 5 wherein said first and second control plates each comprises a pair of plates, a separate set of said control electrodes being formed on one broad surface of each of said plates, the opposite broad surface of each of said plates having a single overall electrode thereon and a resistive material on the walls of said apertures interconnecting the electrodes on the opposite surfaces of said plates, said means for applying potentials to said control electrodes including means for applying a forward biasing potential between the ends of the apertures through which electron flow is desired.
 7. The device of claim 6 wherein said resistive material is secondary emissive.
 8. The device of claim 5 wherein the first and second sets of control electrodes of said second of said control plates each respectively encompass single rows and columns of said apertuRes.
 9. The device of claim 5 wherein the electrode strips of said second of said control plates positioned opposite corresponding aperture portions of the electrode strips of said first of said control plates are connected together so as to form corresponding portions of the symbols. 